Photoacid generators, photoresist compositions containing the same and pattering method with the use of the compositions

ABSTRACT

Photoacid generators comprising sulfonium salt compounds represented by the following general formula (2) wherein R 1  and R 2  represent each an alkyl group optionally having oxo, or R 1  and R 2  may be cyclized together to form an alkylene group optionally having oxo; R 3 , R 4  and R 5  represent each hydrogen or a linear, branched, monocyclic, polycyclic or crosslinked cyclic alkyl group; and Y −  represents a counter ion.

TECHNICAL FIELD

[0001] The present invention relates to a photoacid generator, aphotoresist composition containing the same and a pattering method usingthe composition. More particularly, it relates to a photoacid generatorsuitable for photolithography using a far UV ray, typically representedby an ArF excimer laser, as a ray of light for exposing, a photoresistcomposition containing the photoacid generator, and a pattering methodusing the composition.

BACKGROUND ART

[0002] In manufacture of semiconductor devices such as typical LSIs(Large Scale Integrated circuits), photolithography technology isnecessarily used to pattern insulating films such as silicon oxide andsilicon nitride films formed on a semiconductor substrate into desiredshapes. It is also used to pattern conductive films such as aluminumalloy and copper alloy films and a work itself including thesemiconductor substrate.

[0003] In the photolithography, a UV-sensitive photoresist is applied onthe work to form a photoresist film, to which a UV ray is radiated(which is exposed to a UV ray) through a mask pattern to turn aUV-radiated region into a soluble one (positive type) or an insolubleone (negative type). The photoresist film is then subjected to adeveloping process to partially remove the soluble one with a solventfor forming a resist pattern. Then, using the resist pattern as a mask,the work is selectively etched for patterning.

[0004] As an LSI is required to have a higher degree of functionalityand performance, it is carried out to achieve a higher concentration andintegration. Therefore, a need for photolithography technology to formfine circuit patterns becomes stricter. As a means for fine patterning,it is known to shorten a wavelength of a lithographic source forgenerating an exposing ray of light. For example, in mass production ofa DRAM (Dynamic Random Access Memory) of 256 M bits through 1 G bits(its process size ranging from 0.25 μm to 0.15 μm), a far UV rayconsisting of a KrF excimer laser ray of shorter wavelength (wavelength:248 nm) is used instead of a UV ray consisting of an i-ray of theconventional type (wavelength: 365 nm).

[0005] In manufacture of a DRAM with an integration density of 4 G bitsor greater (its process size being equal to 0.15 μm or less) thatrequires a fine pattern technology, a light source is required toradiate a far UV ray with a much shorter wavelength. In such a case, itis considered effective to use an ArF excimer laser ray (wavelength: 193nm) and an F₂ excimer laser ray (wavelength: 157 nm) inphotolithography.

[0006] In particular, the photolithography using an ArF excimer laserray (ArF excimer laser lithography) is an effective candidate for thenext-generation fine patterning technology following to the KrF excimerlaser lithography and is now increasingly studied. For example, Takechiet al., Journal of Photopolymer Science and Technology, vol. 5, No. 3,pp. 439-446 (1992); R. D. Allen et al, Journal of Photopolymer Scienceand Technology, vol. 8, No. 4, pp. 623-636 (1995) and vol. 9, No. 3, pp.465-474 (1996).

[0007] In addition to a high resolution corresponding to themicro-patterned process size, a high sensitivity is required for theresists for lithography using the above-mentioned ArF and F₂ excimerlasers, due to background situations such as a gas for use as a rawmaterial in the laser oscillation having a short lifetime, an expensivelens being necessary, and the lens being able to be damaged easily bythe laser. High sensitive photoresists suitable for such needs include awell-known chemically amplified resist that utilizes a photoacidgenerator as a photosensitive agent. The chemically amplified resist hasa characteristic that allows the photoacid generator contained thereinto generate a protonic acid due to light radiation. The protonic acidcauses an acid catalytic reaction with a base resin and so forth in theresist by heating treatment after exposure. As a result, an extremelyhigh sensitivity is achieved compared to that of a conventional resistthat has a photoreaction efficiency rate (a reaction number per photon)less than 1.

[0008] As a typically known example of the chemically amplified resist,JP 2-27660A publication discloses a resist consisting of a combinationof triphenylsulfonium hexafluoroarsenate andpoly(p-tert-butoxycarbonyloxy-α-methylstyrene). Most of currentlydeveloped resists are of the chemically amplified type and thusdevelopment of high sensitive materials corresponding to shortenedwavelengths of exposing sources is essentially required.

[0009] The above-mentioned chemically amplified resists used areclassified into the positive and negative types. Among those, thechemically amplified resists of the positive type comprise at leastthree components: (1) a photoacid generator; (2) a base resin containinga group decomposable with acids; and (3) a solvent. On the other hand,the chemically amplified resists of the negative type are classifiedinto two: one that essentially requires a crosslinking agent; and theother that requires no crosslinking agent. The former comprises at leastfour components: (1) a photoacid generator; (2) a base resin capable ofreacting with a crosslinking agent; (3) a crosslinking agent; and (4) asolvent. The latter comprises at least three components: (1) a photoacidgenerator; (2) a base resin containing a crosslinking group; and (3) asolvent.

[0010] Examples of the photoacid generator that serves an important rolein such chemically amplified resists include triphenylsulfonium saltderivatives as described in Journal of the Organic Chemistry, vol.43(No. 15), pp. 3055-3058 (1978); alkylsulfonuim salt derivatives such ascyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate asdisclosed in JP 7-28237A publication; and diphenyliodonium saltderivatives and succinimide derivatives as described in Journal of thePolymer Science, vol. 56, pp. 383-395 (1976).

[0011] Particularly, in the ArF excimer laser lithography, the mostwidely used photoacid generators at present are sulfonium saltcompounds. Among those, triphenylsulfonium salt derivatives are mostwidely used currently. For example, see Nozaki et al., Journal ofPhotopolymer Science and Technology, vol.10 (No.4), pp.545-550(1997);and Yamachika et al.,Journal of Photopolymer Science and Technology,vol. 12 (No. 4), pp. 553-560 (1999).

[0012] One of important technical subjects on the resists for use in thelithography that uses a short-wavelength exposing source, represented bythe ArF excimer laser, is to provide improved transparency to theexposing light of ray. This is because poor transparency lowers theresolution of the resist and worsens the pattern shape with trailingedges.

[0013] From such a viewpoint, unfortunately, though the above-mentionedtriphenylsulfonium salt derivative is most widely used at present in theArF excimer laser lithography as the photoacid generator consisting of asulfonium salt compound, it has a disadvantage because its transparencyis poor. That is, the triphenylsulfonium salt derivative has a benzenering and thus strongly absorbs far UV rays not greater than 220 nm suchas the ArF excimer laser characteristically. Accordingly, thetriphenylsulfonium salt derivative is used as the photoacid generator tocause lower transparency of the resist. For example, see Naitoh Takuya,The 8th Research Group on Polymers for Microelectronics and Photonics,Proceedings, pp. 16-18 (1999).

[0014] Therefore, alkylsulfonium salt2-oxocyclohexyl-methyl(2-norbornyl)sulfonium trifluoro methanesulfonate(NEALS), and cyclohexylmethyl(2-oxocyclo hexyl)sulfoniumtrifluoromethanesulfonate (ALS) are finally developed as new photoacidgenerators that are highly transparent against the ArF excimer laser.For example, see Proceeding of SPIE, vol. 2195, pp. 194-204 (1994); andProceeding of SPIE, vol. 2438, pp. 433-444 (1995).

[0015] Though the above-mentioned newly developed photoacid generatorsconsisting of sulfonium salt derivatives such as NEALS and ALS canimprove transparency, they have disadvantages in sensitivity and thermalstability.

[0016] As for the sensitivity, in the ArF excimer laser lithography, arate of sensitivity (exposure amount) of 20 mJ/cm² and below (ideally of10 mJ/cm² and below) is required in general, though the above-mentionedNEALS requires an exposure amount of 50 mJ/cm² and above. Therefore,lowered sensitivity can not be avoided. On the other hand, as for thethermal stability, a thermal decomposition point in a resist film(resinous film) is about 120° C. and below, the upper temperature at thesteps of heating during film formation of and after exposure to theresist is limited to about 120° C. In the resists in which theabove-mentioned sulfonium salt derivatives are used as the photoacidgenerators, a process of heating at about 125° C. and above is requiredto release an acid even from unexposed parts by decomposition. Thisheating is impossible and their thermal stability lowers.

DISCLOSURE OF INVENTION

[0017] The present invention has been made in consideration of theabove-mentioned situation and accordingly has an object to provide aphotoacid generator capable of improving transmissivity and ofpreventing reduction of sensitivity and thermal stability, a photoresistcomposition containing the same and a method of pattering using thecomposition.

[0018] To solve the above-mentioned subject, the invention as describedin claim 1 relates to a photoacid generator, comprising a sulfonium saltcompound represented by general formula (1):

[0019] wherein R represents an alkylene group with or without an oxogroup; R³, R⁴and R⁵repsesent a hydrogen atom or a straight chain,branched, monocyclic, polycyclic or bridged cyclic alkyl group, and Y⁻represents a counter ion.

[0020] The invention as described in claim 2 relates to the photoacidgenerator according to claim 1, wherein R represents a alkylene grouphaving 4 to 7 carbon atoms with or without an oxo group; R³, R⁴ and R⁵represent a hydrogen atom or a straight chain, branched, monocyclic,polycyclic or bridged cyclic alkyl group having 1 to 12 carbon atoms inthe general formula (1).

[0021] The invention as described in claim 3 relates to a photoacidgenerator, comprising a sulfonium salt compound represented by generalformula (2):

[0022] wherein R¹ and R² represent an alkyl group with or without an oxogroup, or their cyclic alkylene group with or without an oxo group; R³,R⁴ and R⁵ represent a hydrogen atom or a straight chain, branched,monocyclic, polycyclic or bridged cyclic alkyl group, and Y⁻ representsa counter ion.

[0023] The invention as described in claim 4 relates to the photoacidgenerator according to claim 3, comprising a sulfonium salt compound,wherein R¹ and R²represent a alkyl group having 1 to 12 carbon atomswith or without an oxo group, or their cyclic alkylene group having 4 to7 carbon atoms group with or without an oxo group; and R³, R⁴and R ⁵represent a hydrogen atom or a straight chain, branched, monocyclic,polycyclic or bridged cyclic alkyl group having 1 to 12 carbon atoms inthe general formula (2).

[0024] The invention as described in claim 5 relates to the photoacidgenerator according to any one of claims 1-2, comprising a sulfoniumsalt compound, wherein the counter ion represented by Y⁻ is Z—SO₃ ⁻ (Zrepresents C_(n)F_(2n+1) (n is 1-8), an alkyl group, analkyl-substituted or non-substituted aromatic group), BF₄ ⁻, AsF₆ ⁻,SbF₆ ⁻, ClO₄ ⁻, Br⁻, Cl⁻ or I⁻ in the general formula (1).

[0025] The invention as described in claim 6 relates to the photoacidgenerator according to any one of claims 3-4, comprising a sulfoniumsalt compound, wherein the counter ion represented by Y⁻ is Z—SO₃ ⁻ (Zrepresents C_(n)F_(2n+1) (n is 1-8), an alkyl group, analkyl-substituted or non-substituted aromatic group), BF₄ ⁻, AsF₆ ⁻,SbF₆ ⁻, ClO₄ ⁻, Br⁻, Cl⁻ or I⁻ in the general formula (2).

[0026] The invention as described in claim 7 relates to a positive-typephotoresist composition, containing the photoacid generator according toany one of claims 1-4.

[0027] The invention as described in claim 8 relates to a negative-typephotoresist composition, containing the photoacid generator according toany one of claims 1-4.

[0028] The invention as described in claim 9 relates to a method ofpatterning, comprising the steps of: applying the photoresistcomposition according to claim 7 on a substrate to be processed;exposing said substrate to a ray of light with a wavelength of about 300nm or below; and developing said substrate.

[0029] The invention as described in claim 10 relates to the method ofpatterning according to claim 9, wherein said ray of light for exposingis a KrF excimer laser.

[0030] The invention as described in claim 11 relates to the method ofpatterning according to claim 9, wherein said ray of light for exposingis an ArF excimer laser.

[0031] The invention as described in claim 12 relates to the method ofpatterning according to claim 9, wherein said ray of light for exposingis a F₂ excimer laser.

[0032] The invention as described in claim 13 relates to a method ofpatterning, comprising the steps of: applying the photoresistcomposition according to claim 8 on a substrate to be processed;exposing said substrate to a ray of light with a wavelength of about 300nm or below; and developing said substrate.

[0033] The invention as described in claim 14 relates to the method ofpatterning according to claim 13, wherein said ray of light for exposingis a KrF excimer laser.

[0034] The invention as described in claim 15 relates to the method ofpatterning according to claim 13, wherein said ray of light for exposingis an ArF excimer laser.

[0035] The invention as described in claim 16 relates to the method ofpatterning according to claim 13, wherein said ray of light for exposingis a F₂ excimer laser.

BRIEF DESCRIPTION OF DRAWINGS

[0036]FIG. 1 is a diagram showing relations between transmittance andcontents of photoacid generators in photoresist compositions obtained inexamples of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0037] Presumptions:

[0038] Prior to description of embodiments according to the presentinvention, the presumptions for the present invention will be describedgenerally.

[0039] The inventors have intensively studied to achieve theabove-mentioned objects and finally completed the present invention.Namely, according to the present invention, a photoacid generator(sulfonium salt compound) is obtained, which has high transparency tothe ArF excimer laser and thermal stability at about 150° C. or aboveeven in resinous films. Specifically, the present invention is based onthe finding that the above-mentioned subject can be solved by aphotoacid generator consisting of a new alkylsulfonium salt compoundwith a structure disclosed below, a photoresist composition containingthe photoacid generator as a component and a method of patterning inwhich patterning is carried out by light radiation using the photoresistcomposition.

[0040] In the above general formula (2), R¹ and R² may comprise an alkylgroup or an alkyl group having an oxo group, or their cyclic alkylenegroup or their cyclic alkylene group having an oxo group.

[0041] Examples of the alkyl group include methyl group, ethyl group,propyl group, isopropyl group, butyl group, sec-butyl group, tert-butylgroup, 2-methy-butyl group, 3-methy-butyl group, 3,3-dimethy-butylgroup, pentyl group, 2-methyl-pentyl group, 3-methyl-pentyl group,4-methyl-pentyl group, 4,4-dimethyl-pentyl group, 2-ethyl-pentyl group,3-ethyl-pentyl group, hexyl group, 3-methyl-hexyl group, 4-methyl-hexylgroup, 5-methyl-hexylgroup, 5,5-dimethyl-hexyl group, 2-ethyl-hexylgroup, 3-ethyl-hexyl group, 4-ethyl-hexyl group, heptyl group,2-methyl-heptyl group, 3-methyl-heptyl group, 4-methyl-heptyl group,5-methyl-heptyl group, 6-methyl-heptyl group, 6,6-dimethyl-heptyl group,2-ethyl-heptyl group, 3-ethyl-heptyl group, 4-ethyl-heptyl group,5-ethyl-heptyl group, 2-ethyl-heptyl group, 3-ethyl-heptyl group,4-propyl-heptyl group, octyl group, 2-methyl-octyl group, 3-methyl-octylgroup, 4-methyl-octyl group, 5-methyl-octyl group, 6-methyl-octyl group,7-methyl-octyl group, 7,7-dimethyl-octyl group, 2-ethyl-octyl group,2-ethyl-octyl group, 3-ethyl-octyl group, 4-ethyl-octyl group,5-ethyl-octyl group, cyclopentyl group, cyclohexyl group, cycloheptylgroup, cyclopropylmethyl group, methylcyclohexyl group, cyclohexylmethylgroup, norbornyl group, tricyclodecyl group (in particular, tricyclo[5.2.1.0^(2,6)]decyl group), adamantyl group, bornyl group,tetracyclododecyl group (in particular, tetracyclo[4.4.0^(2,5).1^(7,10)]dodecyl group).

[0042] Examples of the alkyl group having an oxo group include2-oxo-propyl group, 2-oxo-butyl group, 2-oxo-3-methy-butyl group,2-oxo-3,3-dimethy-butyl group, 2-oxo-pentyl group, 2-oxo-3-methyl-pentylgroup, 2-oxo-3,3-dimethyl-pentyl group, 2-oxo-4-methyl-pentyl group,2-oxo-4,4-dimethyl-pentyl group, 2-oxo-3-ethyl-pentyl group,2-oxo-3,3-diethyl-pentyl group, 2-oxo-4-methyl-4-ethyl-pentyl group,2-oxo-hexyl group, 2-oxo-3-methyl-hexyl group, 2-oxo-3,3-dimethyl-hexylgroup, 2-oxo-4,4-dimethyl-hexyl group, 2-oxo-5,5-dimethyl-hexyl group,2-oxo-3-ethyl-hexyl group, 2-oxo-4-ethyl-hexyl group, 2-oxo-heptylgroup, 2-oxo-3-methyl-heptyl group, 2-oxo-4-methyl-heptyl group,2-oxo-5-methyl-heptyl group, 2-oxo-6-methyl-heptyl group,2-oxo-6,6-dimethyl-heptyl group, 2-oxo-3-ethyl-heptyl group,2-oxo-4-ethyl-heptyl group, 2-oxo-5-ethyl-heptyl group,2-oxo-3-propyl-heptyl group, 2-oxo-4-propyl-heptyl group, 2-oxo-octylgroup, 2-oxo-3-methyl-octyl group, 2-oxo-4-methyl-octyl group,2-oxo-5-methyl-octyl group, 2-oxo-6-methyl-octyl group,2-oxo-7-methyl-octyl group, 2-oxo-7,7-dimethyl-octyl group,2-oxo-3-ethyl-octyl group, 2-oxo-4-ethyl-octyl group,2-oxo-5-ethyl-octyl group, 2-oxo-cyclopentyl group, 2-oxo-cyclohexylgroup, 2-oxo-cycloheptyl group, 2-oxo-cyclopropylmethyl group,2-oxo-methylcyclohexyl group, 2-oxo-cyclohexylmethyl group,2-oxo-norbornyl group, 2-oxo-tricyclodecyl group (in particular,2-oxo-tricyclo[5.2.1.0^(2,6)]decyl group), 2-oxo-tetracyclododecyl group(in particular, 2-oxo-tetracyclo [4.4.0^(2,5).1^(7,10)]dodecyl group),2-oxo-bornyl group, 2-oxo-2-cyclohexyl-ethyl group and2-oxo-2-cyclopentyl-ethyl group.

[0043] Examples of the cyclic alkylene group include propylene group,butylene group, pentylene group, hexylene group, heptylene group,oxopropylene group, oxobutylene group, oxopentylene group, oxohexylenegroup and oxoheptylene group.

[0044] R³, R⁴ and R⁵ represent a hydrogen atom or a straight chain,branched, monocyclic, polycyclic or bridged cyclic alkyl group having 1to 12 carbon atoms. Examples of the straight chain, branched,monocyclic, polycyclic or bridged cyclic alkyl group having 1 to 12carbon atoms include methyl group, ethyl group, propyl group, isopropylgroup, butyl group, sec-butyl group, tert-butyl group, 2-methy-butylgroup, 3-methy-butyl group, 3,3-dimethy-butyl group, pentyl group,2-methyl-pentyl group, 3-methyl-pentyl group, 4-methyl-pentyl group,4,4-dimethyl-pentyl group, 2-ethyl-pentyl group, 3-ethyl-pentyl group,hexyl group, 3-methyl-hexyl group, 4-methyl-hexylgroup,5-methyl-hexylgroup, 5,5-dimethyl-hexyl group, 2-ethyl-hexyl group,3-ethyl-hexyl group, 4-ethyl-hexyl group, heptyl group, 2-methyl-heptylgroup, 3-methyl-heptyl group, 4-methyl-heptyl group, 5-methyl-heptylgroup, 6-methyl-heptyl group, 6,6-dimethyl-heptyl group, 2-ethyl-heptylgroup, 3-ethyl-heptyl group, 4-ethyl-heptyl group, 5-ethyl-heptyl group,2-ethyl-heptyl group, 3-ethyl-heptyl group, 4-propyl-heptyl group, octylgroup, 2-methyl-octyl group, 3-methyl-octyl group, 4-methyl-octyl group,5-methyl-octyl group, 6-methyl-octyl group, 7-methyl-octyl group,7,7-dimethyl-octyl group, 2-ethyl-octyl group, 2-ethyl-octyl group,3-ethyl-octyl group, 4-ethyl-octyl group, 5-ethyl-octyl group,cyclopentyl group, cyclohexyl group, cycloheptyl group,cyclopropylmethyl group, methylcyclohexyl group, cyclohexylmethyl group,norbornyl group, tricyclodecyl group (in particular, tricyclo[5.2.1.0^(2,6)]decyl group), adamantyl group, bornyl group andtetracyclododecyl group (in particular, tetracyclo[4.4.0^(2,5).1^(7,10)]dodecyl group).

[0045] Y⁻ represents a counter ion. Examples of the counter ion includeBF₄ ⁻ (tetrafluoroborato ion); AsF₆ (hexafluoro aresenate ion); SbF₆ ⁻(hexafluoroantimonate ion); PF₆ ⁻ (hexafluorophosphate ion); ions of asulfonic acid having a fluorocarbon group, such as CF₃SO₃ ⁻(trifluoromethanesulfonate ion), C₂F₅SO₃ ⁻ (pentafluoroethanesulfonateion), C₃F₇SO₃ ⁻ (heptafluoropropanesulfonate ion), C₄F₉SO₃ ⁻ (nonafluorobutanesulfonate ion), C₅F₁₁SO₃ ⁻ (dodecafluoropentanesulfonate ion),C₆F₁₃SO₃ ⁻ (tridecafluorohexanesulfonate ion), C₇F₁₅SO₃ ⁻(pentadecafluoroheptanesulfonate ion), C₈F₁₇SO₃ ⁻ (heptadecafluorooctanesulfonate ion), C₉F₁₉SO₃ ⁻ (nonadecafluorononane sulfonateion) and C₁₀F₂₁SO₃ ⁻ (henycosafluorodecanesulfonate ion); ions of analkylsulfonic acid, such as CH₃SO₃ ⁻ (methanesulfonate ion), C₂H₅SO₃ ⁻(ethanesulfonate ion), C₃H₇SO₃ ⁻ (propanesulfonate ion), C₄H₈SO₃ ⁻(butanesulfonate ion), C₅H₁₁SO₃ ⁻ (pentanesulfonate ion), C₆H₁₃SO₃ ⁻(hexanesulfonate ion), C₇H₁₅SO₃ ⁻ (heptanesulfonate ion), C₈H₁₇SO₃ ⁻(octanesulfonate ion), cyclohexansulfonate ion and camphorsulfonate ion;ions of a sulfonic acid having an aromatic group, such asbenzenesulfonic acid ion, toluenesulfonic acid ion, naphthalenesulfonicacid ion, antracenesulfonic acid ion, fluorobenzenesulfonic acid ion,difluorobenzenesulfonic acid ion, trifluorobenzene sulfonic acid ion,chlorobenzenesulfonic acid ion, dichloro benzenesulfonic acid ion andtrichlorobenzenesulfonic acid ion; ClO₄ ⁻ (perchloric acid ion); Br⁻(bromine ion); Cl⁻ (chlorine ion); and I⁻ (iodine ion).

[0046] A method of synthesizing the sulfonium salt compound representedby general formula (2) according to the present invention is nowexemplified. A sulfide compound represented by general formula (5):

R¹—S—R²  (5)

[0047] is dissolved in acetonitrile, wherein R¹ and R² are the same asabove, followed by adding a halogenated alkyl represented by generalformula (6):

[0048] wherein R³, R⁴ and R⁵ are the same as above; and X reprsents ahalogen atom such as iodine, bromine and chlorine.

[0049] After agitation of the mixture for 0.5-24 hours, an organic metalrepresented by general formula (7):

Y⁻W⁺  (7)

[0050] is added, wherein Y is the same as above; and W represents ametal atom such as potassium, sodium and silver.

[0051] A halogenated metal salt precipitated is subjected to filtrationand then its filtrate is distilled under reduced pressure to remove asolvent therefrom. A residue is rinsed with an appropriate solvent orrecrystallized to obtain the sulfonium salt compound represented bygeneral formula (2).

[0052] The sulfonium salt compound thus obtained and represented bygeneral formula (2) is a new compound and is found to have extremely lowoptical absorption to ArF excimer laser compared to the known photoacidgenerator (triphenylsulfonium trifluoromethanesulfonate (hereinafterreferred to as TPS) as described in the paper by Crivello et al.). Thephotoacid generator developed for KrF excimer laser lithography (TPS asdescribed in the paper by Crivello et al.) has strong optical absorptionto far UV ray such as ArF excimer laser. Therefore, if it is used as aphotoacid generator for an ArF resist, it reduces the transparency ofthe resist remarkably. Compared to such TPS, the sulfonium saltderivatives as disclosed in the present invention have extremely lowoptical absorption to ArF excimer laser and are obviously suitable for acomponent of a resist for ArF excimer laser lithography with respect totransparency to a ray of exposing light. In addition to ArF excimerlaser, they also have high transparency to KrF eximer laser and F₂excimer laser. They can be used as photoacid generators for resistsusing these lasers as rays of exposing light.

[0053] The sulfonium salt compounds of the present invention areconfirmed to have smaller amounts of rays of exposing light to generatean acid, that is, higher sensitivity compared to the conventional hightransparent photoacid generators for ArF excimer laser lithography:alkylsulfonium salt 2-oxocyclohexyl-methyl(2-norbornyl)sulfoniumtrifluoromethanesulfonate(NEALS); andcyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethane sulfonate(ALS). It is also confirmed that they have higher thermal decompositionpoints and more excellent thermal stability compared to NEALS and ALS.

[0054] In the photoresist composition of the present invention, asdescribed above, the chemically amplified resists of the positive typecomprise at least three components: (1) a photoacid generator; (2) abase resin containing a group decomposable with acids; and (3) asolvent. On the other hand, the chemically amplified resists of thenegative type are classified into two: one that essentially requires acrosslinking agent; and the other that requires no crosslinking agent.The former comprises at least four components: (1) a photoacidgenerator; (2) a base resin capable of reacting with a crosslinkingagent; (3) a crosslinking agent; and (4) a solvent. The latter comprisesat least three components: (1) a photoacid generator; (2) a base resincontaining a crosslinking group; and (3) a solvent.

[0055] In the photoresist composition of the present invention, thesulfonium salt compound represented by general formula (2) can be usedsolely but may be used in combination of two or more such compounds. Inthe photoresist composition of the present invention, the alkylsulfoniumsalt compound represented by general formula (2) may be containednormally at 0.1-40 weight parts and preferably 1-25 weight parts per 100weight parts of the total solid containing the compound itself. If thecontent is less than 0.1 weight part, the sensitivity of the presentinvention reduces remarkably and patterning is difficult. If it is morethan 40 weight parts, formation of a uniform coating is difficult andresidue or scum is easily generated after development disadvantageously.

[0056] A polymer that has high transparency in a region of far UV rayand contains an unstable group against a functional group and an acidmay be set and used appropriately as a polymeric compound that is aconstituent of the present invention. Namely, polymeric compoundsrepresented by the general formulae (8) - (13) may be used, for example,as described later.

[0057] In the positive-type photoresist composition of the presentinvention, a resin that is highly transparent to an exposing wavelength,specifically a ray of exposing light, for example, ArF excimer laser andthat can be solubilized in an alkaline developer by acidic action can beset and used appropriately. The content of the resin in 100 weight partsof the total components except for the solvent contained in thephotoresist composition maybe normally at 60-99.8weight parts,preferably 75-99 weight parts. Examples of resins preferably used forthe positive-type photoresist composition of the present inventioninclude the following resins. For example, a resin is disclosed in JP2000-26446 A (JP Hei-10-188853 application) and represented by thefollowing general formula (8):

[0058] wherein R⁶, R⁷, R⁸ and R¹⁰ represent a hydrogen atom or a methylgroup; R⁹ represents a group decomposable with an acid, or a bridgedcyclic hydrocarbon group having 7 to 13 carbon atoms having a groupdecomposable with an acid; R¹¹ represents a hydrogen atom, a hydrocarbongroup having 1 to 12 carbon atoms, or a bridged cyclic hydrocarbon grouphaving 7 to 13 carbon atoms having a carboxyl group; x, y and zrepresent arbitrary numbers satisfying x+y+z=1, 0<x<1, 0<y<1, 0≦z<1; andthe polymer has a weight average molecular weight of 2000-200000.

[0059] Another resin is disclosed in Japanese Patent No.2856116. It isrepresented by the following general formula (9):

[0060] wherein R¹², R¹³ and R¹⁴ represent a hydrogen atom or a methylgroup; M represents a group having a bridged cyclic hydrocarbon grouphaving 7 to 13 carbon atoms; R¹² represents a group decomposable with anacid; R¹⁴ represents a hydrogen atom or a hydrocarbon group having 1 to12 carbon atoms; k, m and n represent arbitrary numbers satisfyingk+m+n=1, 0<k<1, 0<m<1, 0≦n <1; and the polymer has a weight averagemolecular weight of 2000-200000.

[0061] A further resin is described in Journal of Photopolymer Scienceand Technology, vol. 10, No. 4, pp. 545-550 (1997). It is represented bythe following general formula (10):

[0062] wherein R¹⁵, R¹⁶ and R¹⁷ represent a hydrogen atom or a methylgroup; R¹² represents a group having a lactone structure; a and brepresent arbitrary numbers satisfying a+b=1, 0<a<1, 0<b <1; and thepolymer has a weight average molecular weight of 2000-200000.

[0063] A further resin is described in Journal of Photopolymer Scienceand Technology, vol. 10, No. 3, pp. 511-520 (1997). It is represented bythe following general formula (11):

[0064] wherein c, d and e represent arbitrary numbers satisfyingc+d+e=1, 0≦c<1, 0<d<1, 0<e<1; and the polymer has a weight averagemolecular weight of 2000-200000. As for resist resins of the positivetype other than those herein specifically described, as long as theyhave the above high transparency and reactivity to an acid catalyst,they can be also used preferably. In a resist resin of the negative-typephotoresist composition of the present invention, a resin that is highlytransparent to a ray of exposing light, for example, ArF excimer laserand that can be insolubilized in an alkaline developer by an acidicaction can be set and used appropriately. The content of the resin in100 weight parts of the total components except for the solventcontained in the photoresist composition may be normally at 60-99.8weight parts, preferably 75-99 weight parts. Examples of resinspreferably used for the negative-type photoresist composition of thepresent invention include the following resins.

[0065] For example, a resin is described in Journal of PhotopolymerScience and Technology, vol. 12, No. 3, pp. 487-492 (1999). It isrepresented by the following general formula (12):

[0066] wherein i, j and k represent arbitrary numbers satisfyingi+j+k=1, 0≦i<1, 0<j<1, 0≦k<1; and the polymer has a weight averagemolecular weight of 2000-200000. Another resin is represented by thefollowing general formula (13):

[0067] wherein l, m and n represent arbitrary numbers satisfyingl+m+n=1, 0≦l<1, 0<m<1, 0<n<1; and the polymer has a weight averagemolecular weight of 2000-200000. As for resist resins of the negativetype other than those herein specifically described, as long as theyhave the above high transparency and reactivity to an acid catalyst,they can be also used preferably.

[0068] In order to bridge and insolubilize the resin at an exposed part,a crosslinking agent may be added to the photoresist composition of thenegative type. Preferred crosslinking agents include crosslinking agentsof urea-melamine series and polyfunctional epoxy compounds, for example,hexamethoxy methylmelamine, 1,3,4,6-tetrakis(methoxymethyl)glycoluril,1,3-bis(methoxymethyl)-4,5-bis(methoxymethyl)ethyleneurea and1,3-bis(methoxymethyl)urea. Preferred crosslinking agents are notlimited to those herein exemplified. In addition, they may be usedsolely or in combination of two or more thereof.

[0069] A polyhydric alcohol effective to improve a crosslinking densitymay be added as a crosslinking promoter. Examples of the crosslinkingpromoter include 2,3-dihydroxy-5-hydroxy methylnorbornane,1,4-cyclohexanedimethanol and 3,4,8(9)-trihydroxytricyclodecane.

[0070] Solvents suitable for use in the photoresist composition of thepresent invention include any organic solvents so long as they cansufficiently dissolve the components consisting of a polymeric compound,a sulfonium salt and so forth, and the resulting solution can be used toform a uniform spin-coated film. They may be used solely or incombination of two or more thereof. Specifically, they include n-propylalcohol, isopropyl alcohol, n-butyl alcohol, n-tert alcohol, methylsellosolve acetate, ethylsellosolve acetate, propylene glycolmonoethylether acetate, methyl lactate, ethyl lactate, 2-methoxybutyl acetate,2-ethoxyethyl acetate, methyl pyruvate, ethyl pyruvate, methyl3-methoxypropionate, ethyl 3-methoxy propionate,N-methyl-2-pyrrolidinone, cyclohexane, cyclopentanone, cyclohexanol,methyl ethyl ketone, 1,4-dioxane, ethyleneglycolmonomethylether,ethyleneglycol monomethyl ether acetate, ethyleneglycolmonoethylether,ethyleneglycol monoisopropylether, diethyleneglycol monomethylether anddiethyleneglycoldimethylether. They are not limited to theabove-mentioned examples.

[0071] In addition to the above essential constituents in thephotoresist composition, other components such as surfactants, colors,stabilizers, coating improving agents and dyes may be added, ifrequired. A developer used in the present invention for forming a finepattern may be selected according to the solubility of the polymericcompound used in the present invention from appropriate organicsolvents; mixed solvents thereof; aqueous alkaline solutions withappropriate concentrations; and mixtures of the solutions with organicsolvents. Other components such as a surfactant may be added to thedeveloper, if required. The organic solvents to be used include acetone,methyl ethyl ketone, methyl alcohol, ethyl alcohol, isopropyl alcohol,tetrahydrofuran and dioxane. The alkaline solutions to be used includesolutions or aqueous solutions that contain inorganic alkalis such assodium hydroxide, potassium hydroxide, sodium silicate and ammonium;organic amines such as ethylamine, propylamine, diethylamine,dipropylamine, trimethylamine and triethylamine; and organic ammoniumsalts such as tetramethylammonium hydroxide, tetraethylammoniumhydroxide, trimethylhydroxymethylammonium hydroxide,triethylhydroxymethylammonium hydroxide andtrimethylhydroxyethylammonium hydroxide. They are not limited to theabove-mentioned examples.

[0072] On the basis of the above-mentioned presumptions, embodiments ofthe present invention will now be described with reference to specificExamples.

EXAMPLE 1

[0073] 2-methyl-2-propenyl-thiacyclopentanium trifluoro methanesulfonatewas synthesized. This is represented by the following general formula(14):

[0074] The following synthesis operations were performed under a yellowlamp.

[0075] One g of tetrahydrothiophene was dissolved in 20 ml ofacetonitrile in a 100 ml, three-neck flask. Then, 0.94 g of3-bromo-2-methyl-propene was dropped into the mixture under stirring.After agitation for 1 hour, a solution of 1.8 g of silvertrifluoromethanesulfonate in 20 ml of acetonitrile was dropped into themixture. After agitation for 3 hours, the resulting precipitated silverbromide was filtered. The filtrate was distilled under reduced pressurein an evaporator and the residue was washed three times withdiethylether. Further, it was dissolved in 5 ml of acetone and theresulting solution was dropped into 300 ml of ether under stirring,resulting in a white crystal precipitated. After filtration, 1.4 g of2-methyl-2-propenyl-thiacyclopentanium trifluoromethanesulfonate wasobtained (with a yield of 68.5%). The melting point is 52.6° C.

[0076] Analyzed results by NMR and IR on the synthesized product areshown below:

[0077]¹H-NMR (CDCl₃, inner standard substance: tetramethyl silane):δ(ppm) 1.92 (s, 3H, —CH₃), 2.35-2.47 (m, 4H, —CH₂—), 3.39 (m, 1H,—CH₃—), 3.42 (m, 1H, —CH₂—), 3.95 (S, 4H, S⁺—CH₂—), 5.23 (W, 2H,S⁺—CH₂—C(═CH₂)—).

[0078] IR (KBr tablet, cm⁻¹) 2890 (ν_(C—H)); 1642 (ν_(C═C)); 1442, 1420(ν_(C—H)) ; 1258 (ν_(C—F)); 1158, 1027(ν_(SO3)). Elementary analysis C HS Measured value (wt. %) 36.71 5.30 22.02 Theoretical value (wt. %)36.98 5.17 21.93

[0079] wherein the theoretical value is a calculated value forC₉H₁₅F₃O₃S₂ (MW 292.33).

EXAMPLE 2

[0080] 2-methyl-2-propenyl-thiacyclohexanium trifluoro methanesulfonatewas synthesized. This is represented by the following general formula(15):

[0081] An experiment similar to Example 1 was performed usingpentamethylenesulfide instead of tetrahydrothiophene, resulting in 1.68g of 2-methyl-2-propenyl-thiacyclohexanium trifluoromethanesulfonate(with a yield of 78 %). Analyzed results by IR on the synthesizedproduct are shown below:

[0082] IR (KBr tablet, cm⁻¹) 2961 (ν_(C—H)); 1642 (ν_(C═C)); 1442, 1422(ν_(C—H)) ; 1260 (ν_(C—F)) ; 1152, 1029(ν_(SO3)). Measured value (wt. %)39.33 5.32 20.95 Theoretical value (wt. %) 39.21 5.59 20.93

[0083] wherein the theoretical value is a calculated value forC₁₀H₁₇F₃O₃S₂ (MW 306.35).

EXAMPLE 3

[0084] 2-methyl-2-propenyl-thiacyclohexanium nonafluoro butanesulfonatewas synthesized. This is represented by the following general formula(16):

[0085] The following synthesis operations were performed under a yellowlamp.

[0086] In the same method as that of Example 1, using 2.37 g ofpotassium nonafluorobutanesulfonate instead of 1.8 g of potassiumtrifluoromethanesulfonate, an experiment was performed to synthesize2-methyl-2-propenyl-thiacyclohexanium nonafluorobutanesulfonate, and2.05 g of 2-methyl-2-propenyl-thiacyclohexaniumnonafluorobutanesulfonate was obtained (with a yield of 66.2%). Analyzedresults by IR on the synthesized product are shown below:

[0087] IR (KBr tablet, cm⁻¹) 2952 (ν_(C—H)); 1644 (ν_(C═C)); 1440, 1425ν_(C—H)) ; 1259 (ν_(C—F)) ; 1153, 1029(ν_(SO3)). Elementary analysis C HS Measured value (wt. %) 32.5 3.66 13.63 Theoretical value (wt. %) 33.233.74 13.62

[0088] wherein the theoretical value is a calculated value forC₁₂H₁₅F₉O₃S₂ (MW 442.35).

EXAMPLE 4

[0089] 2-butenyl-thiacyclopentanium trifluoromethane sulfonate wassynthesized. This is represented by the following general formula (17):

[0090] The following synthesis operations were performed under a yellowlamp.

[0091] 2 g of tetrahydrothiophene was dissolved in 20 ml of acetonitrilein a 100 ml, three-neck flask. Then, 2.75 g of crotyl bromide wasdropped into the mixture under stirring. After agitation for 1 hour, asolution of 5.1 g of silver trifluoromethanesulfonate in 20 ml ofacetonitrile was dropped into the mixture. After agitation for 3 hours,the resulting precipitated silver bromide was filtered. The filtrate wasdistilled under reduced pressure in an evaporator and the residue waswashed with diethylether. Further, it was dissolved in 5 ml of acetoneand the resulting solution was dropped into 300 ml of ether understirring, resulting in a white crystal precipitated. After filtration,2.2 g of 2-butenyl-thiacyclopentanium trifluorobutane sulfonate wasobtained (with a yield of 68.5 %). Analyzed results by IR on thesynthesized product are shown below:

[0092] IR (KBr tablet, cm⁻¹) 2940 (ν_(C—H)); 1650 (ν_(C═C)); 1420(ν_(C—H)); 1260 (ν_(C—F)); 1160, 1032(ν_(SO3)). Elementary analysis C HS Measured value (wt. %) 37.00 5.20 21.77 Theoretical value (wt. %)36.98 5.17 21.93

[0093] wherein the theoretical value is a calculated value forC₉H₁₅F₃O₃S₂ (MW 292.33).

EXAMPLE 5

[0094] 3-methyl-2-butenyl-thiacyclopentanium trifluoro methanesulfonatewas synthesized. This is represented by the following general formula(18):

[0095] The following synthesis operations were performed under a yellowlamp.

[0096] 2 g of tetrahydrothiophene was dissolved in 20 ml of acetonitrilein a 100 ml, three-neck flask. Then, 2.98 g of bromomethylbutene wasdropped into the mixture under stirring. After agitation for 1 hour, asolution of 5.1 g of silver trifluoromethanesulfonate in 20 ml ofacetonitrile was dropped into the mixture. After agitation for 3 hours,the resulting precipitated silver bromide was filtered. The filtrate wasdistilled under reduced pressure in an evaporator and the residue waswashed with diethylether. Further, it was dissolved in 5 ml of acetoneand the resulting solution was dropped into 300 ml of ether understirring, resulting in a white crystal precipitated. After filtration,2.2 g of 3-methyl-2-butenyl-thiacyclopentanium trifluoromethanesulfonate was obtained (with a yield of 68.5 ).Analyzed resultsby IR on the synthesized product are shown below:

[0097] IR (KBr tablet, cm⁻¹) 2982 (ν_(C—H)); 1650 (ν_(C—C)); 1450, 1429ν_(C—H)); 1264 (ν_(C—F)); 1160, 1030(ν_(SO3)). Elementary analysis C H SMeasured value (wt. %) 39.25 5.59 20.81 Theoretical value (wt. %) 39.215.59 20.93

[0098] wherein the theoretical value is a calculated value forC₁₀H₁₇F₃O₃S₂ (MW 306.35).

EXAMPLE 6

[0099] 2-methyl-1-propenyl-diethylsulfonium trifluoromethane sulfonatewas synthesized. This is represented by the following general formula(19):

[0100] The following synthesis operations were performed under a yellowlamp.

[0101] 1.5 g of diethylsulfide was dissolved in 20 ml of acetonitrile ina 100 ml, three-neck flask. Then, 2.5 g of bromomethylbutene was droppedinto the mixture under stirring. After agitation for 1 hour, a solutionof 4.2 g of silver trifluoromethanesulfonate in 20 ml of acetonitrilewas dropped into the mixture. After agitation for 3 hours, the resultingprecipitated silver bromide was filtered. The filtrate was distilledunder reduced pressure in an evaporator and the residue was washed withdiethylether. Further, it was dissolved in 5 ml of acetone and theresulting solution was dropped into 300 ml of ether under stirring,resulting in a white crystal precipitated. After filtration and thenre-crystallization in ethyl acetate, 3.2 g of2-methyl-1-propenyl-diethylsulfonium trifluoromethanesulfonate wasobtained (with a yield of 65.9 %). Analyzed results by IR on thesynthesized product are shown below:

[0102] IR (KBr tablet, cm⁻¹) 2982 (ν_(C—H)); 1650 (ν_(C═C)); 1447, 1429(ν_(C—H)); 1264 (ν_(C—F)); 1160, 1030(ν_(SO3)). Elementary analysis C HS Measured value (wt. %) 36.72 5.82 21.78 Theoretical value (wt. %)36.94 5.74 22.03

[0103] wherein the theoretical value is a calculated value forC₉H₁₇F₃O₃S₂ (MW 294.3).

Experimental Example 1

[0104] Evaluation on Thermal Stability in Resinous Films

[0105] Films (0.4 μm thick) of poly(methyl methacrylate 40-tert-butylmethacrylate 40- methacrylic acid 20) each containing 1 wt. %of the respective photoacid generators obtained in Examples 1-5 wereheated on a hot plate at a predetermined temperature for 60 seconds.Immediately after heating, they were cooled down to room temperature andthen immersed for 60 seconds into a developer (2.38 wt. %tetramethylammoniumhydroxide (an aqueous solution of TMAH)). As aresult, decomposition points corresponding to the photoacid generatorswere obtained as shown in Table 1.

[0106] When a sulfonium salt compound is decomposed thermally, an aciddecomposes a protection group (tert-butyl group) of the resin to makethe resin soluble in the developer. Accordingly, when the resinous filmis heated and dissolved in the developer, the heating temperature isdefined as the thermal decomposition point of the sulfonium saltcompound in the resinous film. As obvious from Table 1, the thermaldecomposition point of the sulfonium salt compound in the resinous filmobtained in Example 1 of the present invention is 135° C., which is moreexcellent in thermal stability than 2-oxocyclohexylmethyl(2-norbornyl)sulfonium triflate (with a thermal decomposition point of125° C.). TABLE 1 Decomposition Photoacid generator point Photoacidgenerator obtained in Example 1 153° C. Photoacid generator obtained inExample 2 151° C. Photoacid generator obtained in Example 3 155° C.Photoacid generator obtained in Example 4 152° C. Photoacid generatorobtained in Example 5 153° C.2-oxocyclohexylmethyl(2-norbornyl)sulfonium 125° C. triflate

[0107] Experimental Example 2

[0108] Measurement of Transmittance of Resinous Film ContainingAlkylsulfonium Salt

[0109] 1.5 g of polymethyl methacrylate (PMMA) and the sulfonium saltsobtained in Example 1 and 5 were dissolved in ethyl lactate, then theresulting solution was filtered through a membrane filter, further thefiltrate was rotationally coated on a 3-inch quartz substrate, andfinally the coated sample was heated on a hot plate at 120° C. for 60seconds. Through these operations, a resinous film with a thickness ofabout 0.5 μm was obtained. As for the film obtained, the transmittanceat 193.4 nm was measured using a visible UV spectrophotometer (UV-365).Also as for a comparative example of a resinous film that containstriphenylsulfonium trifluoromethanesulfonate (TPS) with benzene ring(s),the transmittance was measured. It can be found from measured resultsshown in FIG. 1 that the resinous films containing the sulfonium saltsobtained in Examples 1-6 exhibit less reduction in transmittance thanthe resinous film that contains triphenylsulfonium trifluoromethanesulfonate.

Experimental Example 3

[0110] Evaluation on Patterning by Positive Resists Using SulfoniumSalts

[0111] A resist consisting of the following composition was prepared:

[0112] (a) 2 g of a resin having a structure represented by thefollowing formula (20);

[0113] (b) 0.02 g of a photoacid generator (the photoacid generatorsobtained in Examples 1-6); and

[0114] (c) 11.5 g of propyleneglycolmonomethylether acetate.

[0115] The above mixture was filtered using a 0.2 μm Teflon (trademark)filter to prepare a resist. The resist was spin-coated over a 4-inchsilicon substrate and baked at 130° C. for 1 minute on a hot plate toform a thin film with a thickness of 0.4 μm. The wafer coated with theresist was placed stationarily in a fully nitrogen-purged contact-typeexposure experimental machine. A mask that had chromium patternsdepicted on a quartz plate was tightly contacted on the resist film,which was exposed through the mask with ArF excimer laser. Immediatelyafter exposure, it was baked at 110° C. for 60 seconds on a hot plate,developed by an immersion technology in an aqueous solution of 2.38%TMAH at a solution temperature of 23° C., subsequently rinsed with purewater for 60 seconds. Obtained was a pattern of the positive type, fromwhich only exposed parts of the resist film were dissolved in thedeveloper and removed.

[0116] As Comparative examples, resists that used2-oxocyclohexylmethyl(2-norbornyl) sulfonium triflato (NEALS) andtriphenylsulfonium trifluoromethanesulfonate (TPS) for photoacidgenerators were evaluated in a similar way. Table 2 shows results onsensitivity and resolution. As obvious from Table 2, the photoresistcompositions of the positive type using the sulfonium salts of thepresent invention are excellent in resolution. TABLE 2 ResolutionSensitivity (μmL/S) (mJ/cm³) Resist containing Photoacid 0.17 7.5generator in Example 1 Resist containing Photoacid 0.17 9 generator inExample 2 Resist containing Photoacid 0.16 8.5 generator in Example 3Resist containing Photoacid 0.17 7.7 generator in Example 4 Resistcontaining Photoacid 0.17 7.6 generator in Example 5 Resist containingPhotoacid 0.19 12.3 generator in Example 6 Comparative example 1 (Resist0.19 50.8 containing NEALS) Comparative example 2 (Resist 0.19 6.5containing TPS)

Experimental Example 4

[0117] Evaluation on Patterning by Negative Resists Using SulfoniumSalts

[0118] A resist consisting of the following composition was prepared:

[0119] (a) 2 g of a resin having a structure represented by thefollowing formula (21);

[0120] (b) 0.04 g of a photoacid generator (the sulfonium salts obtainedin Examples 1-3);

[0121] (c) 0.3 g of 2,3-dihydroxy-5-hydroxymethylnorbornane; and

[0122] (d) 11.5 g of ethyl lactate.

[0123] The above mixture was filtered using a 0.2 μm Teflon filter toprepare a resist. The resist was spin-coated over a 4-inch siliconsubstrate and baked at 80° C. for 1 minute on a hot plate to form a thinfilm with a thickness of 0.4 μm. The wafer coated with the resist wasplaced stationarily in a fully nitrogen-purged contact-type exposureexperimental machine. A mask that had chromium patterns depicted on aquartz plate was tightly contacted on the resist film, which was exposedthrough the mask with ArF excimer laser. Immediately after exposure, itwas baked at 130° C. for 60 seconds on a hot plate, developed by animmersion-technology in an aqueous solution of 2.38% TMAH at a solutiontemperature of 23° C., subsequently rinsed with pure water for 60seconds. Obtained was a pattern of the negative type, from which onlyunexposed parts of the resist film were dissolved in the developer andremoved.

[0124] As Comparative examples, resists of the negative type that used2-oxocyclohexyl methyl(2-norbornyl)sulfonium triflato (NEALS) andtriphenyl sulfonium trifluoromethanesulfonate (TPS) were evaluated in asimilar way. Table 3 shows results on sensitivity and resolution. Asobvious from Table 3, the photoresist compositions of the negative typeusing the sulfonium salts of the present invention are excellent inresolution. TABLE 3 Resolution Sensitivity (μmL/S) (mJ/cm³) Resistcontaining Sulfonium salt in 0.18 7.8 Example 1 Resist containingSulfonium salt in 0.18 8.8 Example 2 Resist containing Sulfonium salt in0.17 8.9 Example 3 Comparative example 1 (Resist 0.20 49 containingNEALS) Comparative example 2 (Resist 0.19 6.8 containing TPS)

[0125] The embodiments consistent with the present invention withreference to the drawing have been described as mentioned above, butspecific configurations are not limited to the above-mentionedembodiments. Modification and variations consistent with the inventioncan be contained within the scope of the appended claims. For example,the present invention is exemplified particularly in application to theproduction of semiconductor devices in the description, though it is notlimited to these and is rather applicable similarly to fields thatrequire micro processing of various conductors and insulators. Inaddition, the synthesis conditions and so forth indicated in Examplesare just exemplification and can be altered in accordance with thepurpose, use and the like.

INDUSTRIAL APPLICABILITY

[0126] As obvious from the forgoing, according to the photoacidgenerator, the photoresist composition containing the photoacidgenerator, and the method of patterning using the photoresistcomposition, such sulfonium salt compounds can be obtained that areexcellent in transparency to far UV rays, typically represented by ArFexcimer laser. In addition, the resist that uses the sulfonium saltcompound as the photoacid generator can be excellent in resolution.

[0127] Therefore, the present invention can provide a photoacidgenerator capable of improving transmittance and of preventing reductionof sensitivity and thermal stability, a photoresist compositioncontaining the same and a method of pattering using the composition.

1. A photoacid generator, comprising a sulfonium salt compoundrepresented by general formula (1):

wherein R represents an alkylene group with or without an oxo group; R³,R⁴ and R⁵ represent a hydrogen atom or a straight chain, branched,monocyclic, polycyclic or bridged cyclic alkyl group, and Y— representsa counter ion.
 2. The photoacid generator according to claim 1, whereinR represents a alkylene group having 4 to 7 carbon atoms with or withoutan oxo group; R³, R⁴ and R⁵ represent a hydrogen atom or a straightchain, branched, monocyclic, polycyclic or bridged cyclic alkyl grouphaving 1 to 12 carbon atoms in the general formula (1).
 3. A photoacidgenerator, comprising a sulfonium salt compound represented by generalformula (2):

wherein R¹ and R² represent an alkyl group with or without an oxo group,or their cyclic alkylene group with or without an oxo group; R³, R⁴ andR⁵ represent a hydrogen atom or a straight chain, branched, monocyclic,polycyclic or bridged cyclic alkyl group, and Y— represents a counterion.
 4. The photoacid generator according to claim 3, comprising asulfonium salt compound, wherein R¹ and R² represent a alkyl grouphaving 1 to 12 carbon atoms with or without an oxo group, or theircyclic alkylene group having 4 to 7 carbon atoms with or without an oxogroup; R³, R⁴ and R⁵ represent a hydrogen atom or a straight chain,branched, monocyclic, polycyclic or bridged cyclic alkyl group having 1to 12 carbon atoms in the general formula (2).
 5. The photoacidgenerator according to any one of claims 1-2, comprising a sulfoniumsalt compound, wherein said counter ion represented by Y⁻ is Z—SO₃ ⁻ (Zrepresents C_(n)F_(2n+1) (n is an integer between 1 and 8), an alkylgroup, an alkyl-substituted or non-substituted aromatic group), BF₄ ⁻,AsF₆ ⁻, SbF₆ ⁻, ClO₄ ⁻, Br⁻, Cl⁻ or I⁻ in the general formula (1). 6.The photoacid generator according to any one of claims 3-4, comprising asulfonium salt compound, wherein said counter ion represented by Y⁻ isZ—SO₃ ⁻ (Z represents C_(n)F_(2n+1) (n is an integer between 1 and 8),an alkyl group, an alkyl-substituted or non-substituted aromatic group),BF₄ ⁻, AsF₆ ⁻, SbF₆ ⁻, ClO₄ ⁻, Br⁻, Cl⁻ or I⁻ in the general formula(2).
 7. A positive-type photoresist composition, containing thephotoacid generator according to any one of claims 1-4.
 8. Anegative-type photoresist composition, containing the photoacidgenerator according to any one of claims 1-4.
 9. A method of patterning,comprising the steps of: applying the photoresist composition accordingto claim 7 on a substrate to be processed; exposing said substrate to aray of light with a wavelength of about 300 nm or below; and developingsaid substrate.
 10. The method of patterning according to claim 9,wherein said ray of light for exposing is a KrF excimer laser.
 11. Themethod of patterning according to claim 9, wherein said ray of light forexposing is an ArF excimer laser.
 12. The method of patterning accordingto claim 9, wherein said ray of light for exposing is a F₂ excimerlaser.
 13. A method of patterning, comprising the steps of: applying thephotoresist composition according to claim 8 on a substrate to beprocessed; exposing said substrate to a ray of light with a wavelengthof about 300 nm or below; and developing said substrate.
 14. The methodof patterning according to claim 13, wherein said ray of light forexposing is a KrF excimer laser.
 15. The method of patterning accordingto claim 13, wherein said ray of light for exposing is an ArF excimerlaser.
 16. The method of patterning according to claim 13, wherein saidray of light for exposing is a F₂ excimer laser.